1. Field of the Invention
The present invention relates to a biodegradable polyester, particularly suitable for extrusion coating, comprising units deriving from at least a diacid and at least a diol, with long chain branches (isometric with respect to the main chains of the polyester) and essentially gel-free, characterized, with respect to conventional biodegradable polyesters of similar viscosity, by higher melt strength, higher breaking stretching ratio, lower neck-in and, moreover, characterized by optimum adhesion to paper, excellent sealability and processability in extrusion coating systems.
The biodegradable polyester according to the invention is obtainable through a reactive extrusion process starting from a polyester precursor comprising units deriving from at least a diacid and at least a diol, substantially linear, with defined viscosity and concentration of reactive sites, preferably such as terminal functional groups which, due to specific reagents capable of reacting with these reactive sites, allow transformation of a few chains of the polyester precursor into isometric branches of this polyester. A further object of the present invention is a laminate product composed of at least a backing, preferably paper, and of at least a first layer composed of polyester according to the invention.
2. State of the Art
Lamination of paper backings with polymer materials is an extremely useful process as it allows improvement of the toughness, water resistance and barrier properties of the paper and it opens further processing options such as heat sealing. However, paper laminates with polymers, such as polyethylene, are not easy to recycle or dispose of, as the polyethylene can only be separated from the paper with great difficulty during the recycling process. Recycling or disposal of the polymer layer removed during treatment thus represents a very serious problem at the end of the life cycle of paper laminates.
US2006/0051603 A1 describes paper laminates with polyesters from diacid-diol. The use of polymers of this type is advantageous as, once separated from the paper, they can be composted. Alternatively, the entire laminate product can be composted. However, US20006/0051603 A1 describes a laminate containing at least two polymer layers composed of two different polyesters having different thermal behaviour and different properties of adhesion to paper.